Thomas Kendall with Waikato (left) and Hongi Hika in London in 1820
In 1815 Kendall's A korao (korero) no New Zealand; or, the New Zealander's first book; being an attempt to compose some lessons for the instruction of the natives was printed in Sydney. This was the first book published in Maori. In 1820 Kendall made an unauthorised visit to England (Marsden had openly appealed to him not to go) accompanied by Hongi Hika and the younger chief Waikato of Rangihoua. The three went to Cambridge to work with Professor Samuel Lee on a compilation of a Maori grammar. The book, A grammar and vocabulary of the language of New Zealand, was published at the end of 1820, and it laid the orthographic foundations of written Maori.
Marsden disapproved of Kendall's interest in Maori language and custom; the mission's role was to impart European religion and civilisation, not to study a 'heathen' culture. Marsden felt that 'by prying into the obscene customs and notions of the natives with a vitiated curiosity, his [Kendall's] own mind has become so polluted that it will be very difficult for him to purify his ideas'. Dismissed after he was found to be having a relationship with a Maori servant, Kendall eventually returned to New South Wales with his family.